Generally, pure diamond is represented as a bonding structure of sp.sup.3 and has an insulating property. However, pure graphite is represented as a bonding structure of sp.sup.2 and has a conductive property because of having delocalized electrons.
In a diamond film of the present invention which will be described in detail herein below, the bonding structure among carbon atoms may be a pure hybrid combination of sp.sup.3 or a mixed combination of sp.sup.2, sp.sup.1, etc. Unlike natural diamond, the fine structure of the diamond film of the present invention may be a polycrystal or an amorphous structure, or a complex structure mixed with a polycrystal and an amorphous structures.
In addition, diamond of the present invention may be composed only of pure carbon atoms, or may be composed of carbon atoms as a main component and impurity atoms such as a metal or a metalloid, etc.
A diamond film which will be described in the present invention covers all of hard carbon, diamond-like carbon, amorphous diamond and nanocrystalline diamond film, etc., without distinguishing from one to another. Further, a diamond film which will be described in the present invention has a meaning of a solid state material which is solidified from a vapor state. A diamond film of the present invention can be used as a good-qualified material for forming an emitter of FED, because it shows a high electron emission property even at a low electric field.
Methods, in prior arts, such as HFCVD (Hot Filament Chemical Vapor Deposition), MPCVD (Microwave Plasma Chemical Vapor Deposition), PECVD (Plasma Enhanced Chemical Vapor Deposition), sputtering, and PLD (Pulse Laser Deposition), etc. have been used forobtaining a diamond film. However, in order to obtain a good-qualified diamond film by using HFCVD or MPCVD method, it is essentially required that the temperature of a substrate must be kept at about from hundreds to 1000.degree. C. Thus, if a material such as glass the melting point of which is below the temperature range required above is used, the use of HFCVD or MPCVD method is difficult. Additionally, a process of HFCVD or MPCVD method is performed at a relatively high temperature, and thus, such a method is not effective in a processing time and an energy efficiency if a diamond film needs to be produced in a large scale.
PECVD method may be available for manufacturing an amorphous diamond film at a room temperature. However, a film manufactured by this PECVD method has a high residual stress and thus there is a disadvantage that a delamination between a substrate and a film may be vulnerable to occurrence depending on a material of the substrate.
Also, a high frequency sputtering method may be used for manufacturing a diamond film at a room temperature. However, in a diamond film manufactured by this sputtering method, it is difficult to obtain a good-qualified diamond film having a preferable electron emission property, compared with the PECVD method.
In addition, a deposition method for manufacturing a diamond film by using a prior art PLD method is described in detail in an article entitled "Deposition of Amorphous Carbon Films from Laser-Produced Plasmas" by C. L. Marquardt, et al., Naval Research Laboratory, Mat. Res. Soc. Symp. Proc. Vol. 38, pp325-335, which was published in 1985. An apparatus for performing this deposition method for manufacturing a diamond film by using a pulse laser can be simply constructed. A good-qualified and excellent film having a high fraction of sp.sup.3 bonding of diamond is possibly manufactured at a room temperature by controlling a power density of laser being irradiated to a target over about 5.times.10.sup.10 watt/cm.sup.2. The power density is equal to a value of energy density per pulse being divided by a pulse width of a pulse laser, while the energy density is value of energy per pulse being devided by a cross-sectional area of laser beams on a target.
However, the PLD method has many limitations in utilization because this method is difficult to manufacture a film having a large area, compared with other methods described above. That is, if a laser having a high energy density is irradiated on a surface of a target being set up in a vacuum, a plume being a mixture of materials such as ions, atoms, molecules, and electrons, etc., which are also constituent components of the target, is formed and expanded to ward a substrate. A vapor material formed by a conventional evaporation method has a distribution which varies depending on cos (.theta.) (.theta. is an angle relative to a normal direction of the target). However, because a plume formed by the PLD method has a distribution which varies depending on cos n(.theta.)(8&lt;n&lt;12), the plume is mainly formed at a limited area around a normal direction of the target which is contacted to the laser beam and thus a film is formed over a small area on the substrate.
That is, when a thin-film is formed on a position of a substrate by solidifying a plume, there exists a problem that the thickness of the thin-film is sharply decreased as the position of the substrate where the plume is to be solidified is placed far apart from a position of where the plume is produced. There exists another problem that when a target made of an alloy composed of various components is used, the thin-film does not have a constant composition in proportion to the constitutional components depending on a position of the target.
In U.S. Pat. No. 4,987,007, granted to S. S. Wagel, et al., in 1991, an apparatus for depositing a diamond film and a manufacturing method thereof are disclosed in detail where carbon ions are extracted from a plasma plume by setting up an ion separation mechanism which includes an accelerating grid electrode, capable of charging and discharging, to a known PLD apparatus. However, the method disclosed in U.S. Pat. No. 4,987,007 above forms only one laser plume and the position on which the plume is to be formed is fixed. Thus, it is difficult to make a film having a large area of more than tens of inches, considering the angular distribution of the laser plume described above.
As a result, it is extremely difficult to manufacture a film having a uniform thickness, composition in constitutional components and a uniform electrical and a mechanical properties, and having a width of more than one inch, if the film is manufactured by the known PLD method which forms only one plume on a fixed position of the target.